Hydrogen bomb explosion. Mushroom cloud produced by the detonation of XX-35 Apache, a 1.85-megaton thermonuclear bomb on 8 July 1956. This was one of a series of detonations carried out during Operation Redwing on the Enewetak and Bikini Atolls in the Marshall Islands of the Pacific Ocean during 1956. Operation Redwing tested the design of actual thermonuclear weapons. XX-35 Apache was a prototype for the XW-27 warhead for a Regulus I missile. The device weighed 1335 kilograms. Although it was a thermonuclear device using fusion, a high proportion of the explosion was due to fission.